1. Field of the Invention
This invention relates generally to tires and more particularly, to tire tread wear indicators.
2. Description of the Related Art
It is known how to provide wear detectors on the tread pattern elements of a tire tread for motor vehicles. One example of a tread wear indicator is shown in FIGS. 1A-C. A tread band 10 includes grooves 13 opening from the front face of the tread band 10, these grooves 13 forming the treads of the tread band 10. Wear indicators 11 are molded into the grooves 13 at a depth m 12, which represents the minimum acceptable depth of the tread grooves 13. FIG. 1B shows the tread band 13 worn down to the wear indicators 11, indicating that the tread band 10 has served its useful life. FIG. 1C is a perspective view of the tread band 10 showing that the tread wear indicators 11 are generally located at the same circumferential location along the tread band 10 so that when the tread is worn down to the wear indicators 11, a wear bar 14 is formed laterally across the tread band 10, which indicates that the useful life of the tread is ended. The undertread 16 portion of the tread band 10 is that portion that is below the bottom of the grooves 13 that are formed in and open to the front face 17 of the tread band 10.
Other examples, of tread wear indicators may be found, for example, in the British patent publications GB-A-2 330 808 and GB-A-2 268 715. These references disclose visual wear detectors consisting of layers of colored light-reflecting rubber that are disposed over the entire circumference of the tire in the mass of the tread. These colored rubber indicators become visible following a given amount of wear on the tire that strips away the rubber covering the colored rubber layers.
Tread bands are used for retreading tires as well as in new tire construction. In either case, the tread band is bonded to a tire casing to provide either a new tire (when bonded to a new tire casing) or a retread tire (when bonded to a used tire casing that has had the old tread buffed off). The tread bands are molded and may be either cured or uncured before being bonded to the tire casing.
The undertread portion of the tread band is typically 2-5 mm thick and may facilitate demolding the tread band. It may further assist in resisting lateral compression of the tread pattern during the process of bonding the tread band to the tire casing. However, this undertread does not provide any useful life for the tread because it lies below the tread grooves that open to the front face of the tread band.
While wear bars are useful indicators of the end of the useful life for the tread, there is a need for improved tread wear indicators that maximize the use of the entire tread band before its end of life.